Field of the Invention
The invention relates to a moldable mass containing graphite and a phase change material, to a process for producing a molding from this mass and to a molding as well as to the use thereof.
In the operation of battery arrangements, in particular of secondary batteries (known as rechargeable batteries or storage batteries), it is important for the battery not to overheat. In particular, the temperature must not rise too much so as not to detract from the service life, energy density and charge capacity of the battery or even cause damage. On the other hand, the stated battery properties can be detracted from even at low temperatures. In particular lithium ion batteries react sensitively to unsuitable operating conditions.
It has in fact been proposed to provide a phase change material (PCM) as an embedding material in a battery arrangement, for example in the form of a battery pack or the like, between the individual battery cells, so as subsequently to cause excess heat to be absorbed in the form of latently stored heat, by way of a phase change of the PCM, if an excessive thermal budget occurs; however, the specific thermal conductivity of the proposed PCMs is very low, and so the charging and discharging dynamic is very low and insufficient for technical application.
For charging and discharging the PCM with heat, to increase the charging and discharging dynamic, graphite has been proposed as a thermally conductive and chemically inert material which is mixed with PCM or into the cavities of which PCM is infiltrated.
Conventionally, cooling packs which contain a graphite/PCM mixture are encased using a stable package so as to prevent liquid PCM from flowing out. However, stable packages of this type are generally not positioned in a positive fit on a battery cell pack, and can only be produced in a range of shapes and sizes at great expense.
U.S. patent publication No. 2003/0054230 A1 discloses a battery module in which a plurality of electrochemical cells, a PCM and a thermally conductive lattice, which may contain graphite inter alia, are brought together in a housing. In accordance with this teaching, a specially manufactured housing is therefore required for each battery arrangement.
Published, European patent application EP 1959212 A2 describes a wall element which forms a latent heat store and which contains two mutually spaced cover plates and a core layer, which fills up the gap between the two cover plates and contains a filling of microcapsules of a phase change material embedded in a plastics material casing (see EP 1959212 A2, abstract). The core layer may additionally contain a pulverulent thermal conductor, such as graphite (see EP 1959212 A2, paragraph [0009]). However, a construction of this type can only be attached to a battery cell pack in a positive fit at great expense.